Typically, equipment used to produce integrated circuits on silicon wafers is referred to as wafer fabrication equipment (WFE). WFE may be generally classified as batch tools, which process a number of wafers simultaneously, or single wafer tools which process wafers individually. In the past, most of the commercially available WFE was designed as batch tools. More recently, the size of silicon wafers, the size of critical features on the wafers, and the complexity of the devices being built has led the industry to produce a much higher percentage of single wafer tools. Of these single wafer tools, a significant number may be classified as cluster tools. A cluster tool consists of a central chamber which houses a robot which serves to manipulate wafers in the tool. The central chamber is typically referred to as a transfer chamber. Around the transfer chamber are located additional chambers which are intended to perform some process on the wafers that are being moved through the system. Also attached to the transfer chamber are one or two load lock chambers. The load lock chambers serve to introduce wafers from the outside environment into the cluster tool.
A cluster tool is typically operated as follows. The transfer chamber is brought to a vacuum by an integrated pumping system. Each of the process chambers are isolated from the transfer chamber by an isolation valve which allows the process chambers to operate at a different level of vacuum than the transfer chamber and prevents any gasses being used in the process chamber from being introduced into the transfer chamber. The load lock chambers are also isolated from the transfer chamber with isolation valves. Each load lock chamber has a door which opens to the outside environment. In normal operation, a cassette loaded with wafers is placed into a load lock chamber through the door and the door is closed. The load lock chamber is then evacuated to the same pressure as the transfer chamber and the isolation valve between the load lock chamber and transfer chamber is opened. The robot in the transfer chamber is moved into position and one wafer is removed from the load lock chamber. The load lock chamber is preferably equipped with an elevator mechanism so as one wafer is removed from the cassette, the elevator moves the stack of wafers in the cassette to position another wafer in the transfer plane so that it can be positioned on the robot blade. The robot in the transfer chamber then rotates with the wafer so that the wafer is aligned with a process chamber position. The process chamber is flushed of any toxic gasses, brought to the same pressure level as the transfer chamber, and the isolation valve is opened. The robot then moves the wafer into the process chamber where it is lifted off the robot. The robot is then retracted from the process chamber and the isolation valve is closed. The process chamber then goes through a series of operations to execute a specified process on the wafer. When complete, the process chamber is brought back to the same environment as the transfer chamber and the isolation valve is opened. The robot removes the wafer from the process chamber and then either moves it to another process chamber for another operation or replaces it in a load lock chamber to be removed from the system when the entire cassette of wafers has been processed.
To improve the productivity of the cluster tools, some wafer manufacturers have automated the loading and unloading of the load lock chambers by including systems that can take a cassette of wafers from a passing vehicle and load it into an open load lock chamber. Similarly, these systems can remove a processed cassette of wafers and place them on a vehicle to be taken to other tools for further processing.
Typically, a cluster tool typically must perform a significant number of functions. The cluster tool must be capable of manipulating wafers through the tool without damaging the wafer or causing particles to be created which may interfere with the function of the process chamber or contaminate the wafer. This wafer handling process includes mechanisms and associated sensors to verify that the wafers have been properly handled. The cluster tool must also be capable of managing the environment of the transfer chamber, the load lock chambers, and each of the process chambers. This involves significant variations in pressure as well as the introduction of a number of different gasses and the creation of plasmas. The tool must also manage the power that is supplied to each of the chambers and provide a control interface to the outside environment which may be a human operator, another control computer, or both.
Currently, cluster tools are designed and built with the following approach. A function or set of functions for the tool is chosen. This dictates the number and type of process chambers that will be attached to the transfer chamber. All of the various systems for wafer handling, pressure control, gas management, power management, and system control hardware are then designed for the specific configuration that is being developed. The computer software that controls the various systems is written so that the tool performs the desired set of processes. Typically, this tool is marketed as a tool to perform the specific functions for which it was designed. The tool is assembled, tested, and delivered to the end users as an integrated unit. The time it takes to complete this design process can be quite lengthy. Modification of any of the intended process functions is difficult because the original tool was designed as an integrated system and any significant changes will necessitate an entirely new design.
Additionally, the manufacture of the tool is somewhat complicated because of the integrated nature of the design. Since the tool controller is designed on the assumption that the tool is one integrated system, it is difficult to test individual portions of the tool. Significant testing must be held until most of the tool is assembled. Because of the complexity of the complete tool, this system test can be a time consuming process. Errors made early in the manufacturing process may not be found until late in testing and may result in a significant amount of effort to correct.
As discussed above, it is customary for cluster tools to be shipped to the end user as a complete unit. The recent move to larger wafer sizes will significantly effect this practice. Equipment designed to accommodate 300mm wafers is too large to be transported economically after assembly. This will necessitate assembly at the fabrication facility for testing, disassembly for shipping, and re-assembly at the end user's site. This additional assembly operation will make tool integration at the end user's site a significantly more involved operation with a much higher costs.
Therefore, there is a need for a modular tool which includes a flexible design and can be assembled, disassembled, reconfigured and reassembled quickly and easily.